Francisco Rosario of Bridgeport wipes his brow as he works in the extreme heat installing temporary fencing for The Gathering of the Vibes music festival at Seaside Park in Bridgeport, Conn. on Monday, July 15, 2013.
Photo: Brian A. Pounds

When two men mingled with a crowd of bystanders and set off two bombs at the Boston Marathon, they killed three people, injured hundreds more and set off a manhunt that shut down a large American city.

They also changed the way security is handled at high-attendance events.

"Certainly, we are mindful of events or incidents at other locations around the country and we work with our local state and federal partners for threat assessments," said Bridgeport Police Chief Joseph Gaudett.

The department is now gearing up for the annual Gathering of the Vibes festival at Seaside Park. The event, which has drawn 20,000 people, will kick off Thursday with more than 40 bands playing on three stages over the course of four days.

Even at events with smaller crowds, experts say, increasing security measures are now an inevitable part of the conversation. The Ives Concert Park in Danbury sees as many as 5,000 people at its summertime events.

Regular attendees of the Alive@Five concert series in Stamford have also seen stricter security checks at the outdoor concert space.

"Part of our enhanced security for the Alive@Five security is the fact that you must factor into everything you do, when planning a public gathering of thousands of people, what happened at the Boston Marathon," said Sandy Goldstein, of the Stamford Downtown Special Services District. "If you don't, you're being irresponsible."

Still, the concert series has had to relax some of its measures as concertgoers have complained and attendance has plummeted.

For example, a requirement that all patrons between the ages of 21 and 25 sign a Consumer Protection Liquor Control Division Age Statement Form -- or a signed statement saying that they are indeed the age that is listed on their ID -- has been relaxed. Now only someone a bartender suspects has a fake identification is asked to fill it out. That measure was an effort to curb underage drinking.

Another security measure, which banned items like umbrellas at Columbus Park, remains. Goldstein said organizers have been trying to find a "happy medium" between keeping people safe and not overreacting to past events.

It's a balancing act that Greenberg said he understands.

At the Ives center, he said, they've held off on changes other locations have instituted, like a ban on backpacks and other items. Instead, they've added stricter inspection protocols and security cameras to their 40-acre venue at Western Connecticut State University.

"We have a responsibility to protect as best as we can," he said.

Instead, the Ives staff works closely with State Police, Western Connecticut State University police and Danbury police on security issues. Those meetings have led to changes in security protocols and the addition of new features, like a security camera system.

"I don't want to go into too much detail because I don't want these things to be tested," Greenberg said.

Inspections of people coming into the park have also been ramped up this year. "It was done (before the Boston event), but not as thoroughly," Greenberg said. "We're checking everything now."

Now in its sixth consecutive year at Seaside, Vibes promoter Ken Hays said thorough inspections of every car, backpack and bag have always been an important part of that festival's security plan.

Despite an increased awareness created by the event in Boston, no substantial changes were made this year because the plan put in place last year was effective, he said.

"We have an extremely thorough and comprehensive police and security deployment in place -- and have for years," Hays said. "We've had multiple meetings with police, fire, EMS and the office of emergency management. The safety of all attendees is paramount and has been for the last 18 years" of Vibes events.

The festival employs private security and the city deploys 35 to 40 officers during the festival's peak times, not including specialized units like the mounted police and a narcotics squad.

"It's a sizable police presence, not only inside the venue, but along the perimeter and the waterfront," Hays said.

Last year, as part of negotiations for a new five-year contract, the Vibes agreed to up its contribution to Bridgeport for police overtime to $250,000, plus an annual 3 percent cost-of-living increase. Before then, the Vibes paid the city just a portion of those costs, despite city officials' claims that the whole tab was taken up by the festival organizers.

Gaudett said the department spends weeks preparing for every event that attracts large crowds, and reviews and analyzes the effectiveness of its strategies after each one.

"For the Puerto Rican Day Parade, for example, Lt. Mark Straubel prepared a 100-page operations plan," he said. "We will be equally prepared for the Vibes."

Security measures have also been adjusted at the festival in the past when incidents big or small have arisen.

That includes a push to prevent the transfer and use of illegal drugs, which stemmed from an FBI investigation of the disappearance of confiscated tanks of nitrous oxide, better known as laughing gas; annual arrests for dealing marijuana, Ecstasy and heroin; and two drug-induced deaths, one in 2009 and another in 2010. "Nitrous, balloons and all illegal substance" is the first of several banned items on lists posted in several places on the festival's website.

A 24-hour hot line created four years ago has also proven a successful tool for meeting people's needs, security or otherwise, Hays said. Attendees can call to report a serious issue or get information about the show, or even campground shower times.

Because planned security measures can only go so far, organizers and officials said they rely on patrons and volunteers to report anything suspicious they may see.

It's something many people are already doing after the tragic event in Boston and mass shootings, like the 2011 incident in Tucson, Ariz, that ended with six dead and 19 injured, including U.S. Rep. Gabrielle Giffords, and the 2012 shooting in an Aurora, Colo., movie theater.

Many Connecticut residents are still reeling from the December massacre of 26 people, most of them children, at Sandy Hook Elementary School in Newtown.